The invention relates to polypeptides which exert the biological activity of GABA B receptors and to nucleic acids encoding these polypeptides, and, in particular, to their use for finding active compounds for crop protection.
Gamma-amino-butyric acid (GABA) is the most important inhibitory neuro-transmitter in the nervous system of vertebrates and invertebrates. The GABA receptors can be classified into two subfamilies, the GABA A and GABA B receptors. Amongst these, the GABA A receptors are ligand-controlled ion channels, while the GABA B receptors are metabotropic, G-protein-coupled receptors. GABA B receptors affect the release of various neurotransmitters and the activity of ion channels.
GABA B receptors have been studied extensively, in particular in vertebrates. Two subtypes (GABA B1 and GABA B2), which are functionally active as heterodimers, are known here (Jones et al., 1998; Kaupmann et al., 1998; White et al., 1998).
In insects, GABA is the most important inhibitory neurotransmitter of the central nervous system. Accordingly, GABA receptors can be detected electrophysiologically on preparations of insect central ganglia. Both the GABA A receptors and the GABA B receptors are the molecular target of important natural and synthetic insecticidally active compounds (Sattelle, 1990; Fukunaga et al., 1999).
The protein sequence of a number of insect GABA A receptors is already known. Thus, the sequences of three different subunits have been described for Drosophila melanogaster (ffrench-Constant et al., 1991; Harvey et al., 1994; Henderson et al., 1993).
The provision of insect GABA B receptors is therefore of great practical importance, for example in the search for new insecticides.
The present invention is therefore based in particular on the object of providing insect GABA B receptors and on assay systems based thereon with a high throughput of test compounds (high throughput screening assays; HTS assays).